1. Field of the Invention
This invention relates to a suspension system for dirigible rear wheels, and more particularly to a rear suspension system for a vehicle in which the rear wheels are dirigible.
2. Description of the Prior Art
There has been known a four-wheel steered vehicle in which the rear wheels are turned in response to turning of the front wheels. When the front wheel turning system and the rear wheel turning system are mechanically connected, the effort required to turn the steering wheel is larger than when only the front wheels are turned in response to turning of the steering wheel.
Generally such a four-wheel steered vehicle is provided with a centering spring mechanism as disclosed, for instance, in Japanese Unexamined Patent Publication No. 63(1988)31880. The centering spring mechanism is provided on a relay rod which connects the left and right rear wheels and is displaced in the transverse direction of the vehicle body to turn the rear wheels, and, in case of failure in the control system of the rear wheel turning system, the force which is transmitted to the relay rods to turn the rear wheels is released and the relay rod is returned to the neutral position, where the rear wheels are held in the straight ahead position, and held there by the centering mechanism. Accordingly, normally the relay rod must be displaced to turn the rear wheels overcoming the force of the centering spring mechanism, which further adds to the effort required to turn the steering wheel.
In the case where a power cylinder mechanism is provided to assist in displacement of the relay rod, the power cylinder mechanism must be large in order to overcome the force of the centering spring mechanism, which adds to the overall size of the rear wheel turning mechanism and complicates the structure of the same.